Perpendicular magnetic recording is a form of magnetic recording in which bits of information are stored in a direction that is perpendicular to the plane of the recording media, which is typically a rotating disk forming part of a disk drive. To obtain this orientation of the bit magnetization, the anisotropy constant of the magnetic recording layer is configured such that its “easy” magnetic axis is perpendicular to the plane of the media. The magnetization establishing each bit is imparted by a write head. The layer in which the bits are formed is typically a magnetically “hard” recording layer. (“Hardness” and “softness” in this context refers to the ability for producing saturation in a magnetic layer with increasing external magnetic fields. A soft layer can produce magnetic saturation significantly faster than a hard layer.) In order to provide an appropriate closed loop for the field created by the write head when writing each bit, the hard recording layer is usually formed atop a “soft” magnetic underlayer (“SUL”).
While the role of the recording layer is to carry the individual bits of recorded data, the role of the SUL is to guide the magnetic write field flux perpendicularly through the recording layer and then through the SUL in a return path to the write head. Often however, the SUL does not sufficiently guide the magnetic write field produced by a write head and is a source of noise. As such, there is a need for a SUL that better guides or enhances the write field and reduces noise.